Cough due to asthma and nonasthmatic eosinophilic bronchitis.

Asthma and nonasthmatic eosinophilic bronchitis are among the most common causes of chronic cough, accounting for about 25 and 10% of cases, respectively. Chronic cough due to asthma may present in isolation in which case it is known as cough-variant asthma. Nonasthmatic eosinophilic bronchitis is characterized by the presence of eosinophilic airway inflammation in the absence of variable airflow obstruction or airway hyperresponsiveness. Both conditions share many immunopathological features with the exceptions to date of mast cell infiltration into the airway smooth muscle, increased IL-13 expression, and narrowing and thickening of the airway wall, which are features reserved to asthma. In most cases the trigger that causes the cough is uncertain. However, removal of potential triggers is important to consider, in particular with respect to occupational exposure to known sensitisers. In both conditions there is subjective and objective improvement following treatment with inhaled corticosteroids, which is associated with the presence of an airway eosinophilia. Whether eosinophilic inflammation is the cause of cough or an epiphenomenon is uncertain, but the failure of anti-IL-5 to modify cough in asthma has questioned a causal association. In asthma, beta-agonist theophylline, leukotriene receptor antagonist, and oral corticosteroid therapy improve cough. In noneosinophilic bronchitis, some patients require oral corticosteroids but the benefit of other additional therapies is unknown. In general, response to therapy in both conditions is very good and the limited long-term data available suggest that both usually have a benign course, although in some cases persistent airflow obstruction may occur.